Art of cracking hydrocarbons



June 8, 1937. E. w. ISOM ART OF CRACKING HYDROCARBONS Filed Sept. 10, 1932 I 'INVE'NTOR Edward 11".} 30/11 TTORNEYS Patented June 8, 1937 UNITED STATES PATENT OFFICE Edward W. Isom, Scarsdale, N. Y., assignor to Sinclair Refining Company, New York, N. Y., a

corporation ofMaine Application September 10, 1932, Serial No. 632,520

4 Claims.

This invention relates to improvements in the manufacture of gasoline by cracking higher boiling hydrocarbon oils. The invention provides, particularly, a process for producing, economical- 5 1y, motor fuel gasoline of improved anti-knock value.

According to the present invention a stream of oil is flowed through two serially connected heating zones without vapor separation in either zone and thence to a vapor separator, the oil stream is heated in the first zone to a high cracking temperature, a secondary stream of oil is introduced into the primary stream of oil flowing from the first to the second heating zone at a rate and temperature eifective substantially to reduce the temperature of the primary stream, the combined oil stream is heated in the second zone to a cracking temperature substantially higher than that to which the oil stream is heated in the first zone, and a temperature effective substantially to inhibit further cracking is maintained in the vapor separator. The secondary stream may approximate, for example, 15 %35% by volume measured at 60 F. of the combined stream. A substantial superatmospheric pressure is maintained on the oil stream in both heating zones and a substantially lower pressure, lower than that under which the oil stream is discharged from the second zone, is maintained in the vapor separator. A residual oil and a distillate fraction including the gasoline product are separated in and taken off from the vapor separator. The oil stream is with advantage heated to a cracking temperature upwards of about 875 F. in the first zone and to a higher cracking temperature, not less than about 40 F. higher than that to which the oil stream is heated in the first zone, in the second zone. The temperature of the primary stream flowing from the first to the second heating zone is with advantage reduced not less than about 40 F. by the introduction of the secondary stream. The temperature in the vapor separator is with advantage limited not to excee about 775 F.

The two heating zones are so proportioned that, at the temperatures attained, the time factor involved in passage of the oil stream through the heating zones is effective to produce substantial cracking in eachof the two heating zones.

These heating zones may consist, with advantage,

of a number of tubes serially connected to form a long heating coil arranged in an appropriate heating furnace. In the first heating zone, some gasoline is formed by cracking. This gasoline is not separated but continues to flow with the oil stream through the second heating zone. In the second heating zone this gasoline, or part of it, is re-formed by cracking at a higher tempera ture than that at which it was formed, the reformed, gasoline being of improved anti-knock value, and at the same time further gasoline is formed by further cracking of the primary oil stream and by cracking of the introduced sec ondary oil stream. The same stock may be supplied to the first heating zone and, as the secondary stream, to the second heating zone, or of two stocks the more refractory may be supplied to the first zone and the less refractory, as the secondary stream, to the second zone. The further cracking in the second heating zone of the primary stream components at temperatures eliectiveto re-form the gasoline formed in the first heating zone tens, in the absence of the introduced secondary stream, to increase the formation of gas and tar with respect to formation of gasoline but, in the presence of the introduced secondary stream, any such increase in the proportionate formation of gas and tar is minimized. Apparently, a particularly advantageous distribution of heat between the re-forming of gasoline formed in the first heating zone, the further cracking of the primary stream and the cracking of the secondary stream is effected in the process of the invention. Further, because of the higher cracking temperature to which the oil stream is heated in the secondary heating zone, the gasoline formed in the second heating zone is itself of improved anti-knock value.

The invention will be further described in connection with the accompanying drawing, which illustrates, diagrammatically and conventionally, in elevation and partly in section and with parts broken away, one form of apparatus adapted for the practice of the process of the invention.

The apparatus illustrated comprises two heating coils I and 2 arranged in the heating flue of a furnace 3, a vapor separator 4, two fractionating towers 5 and 6, a condenser l and a gas separator and receiver 8. The heating furnace comprises a firebox 9 in which fuel is burned communicating through a throat II] with the upper end of the heating flue in which the coils I and 2 are arranged, a fan I! communicating with the lower end of the heating flue in which the coils l and. 2 are arranged and discharging through ducts H and I2, the first for recirculation of heating gases trough the heating flue and the second for discharge to a stack, each of l heating coil 2.

these ducts being provided with appropriate dampers for regulation, and a by-pass opening I3, provided with an appropriate damper for regulation, connecting the throat II] with the heating flue in which the heating coils I and 2 are arranged at a point between these heating coils. The dampered by-pass opening I3 affords control of the distribution of heat supplied from the firebox 9 between the heating coil I andthe A heat exchanger for preheating the air for combustion, supplied through duct I 4, may be arranged in the duct l 2 or in the stack to which this duct connects. Instead of being arranged in a single furnace, the heating coils I and 2 can be arranged in separate'heating furnaces. The fractionating towers 5 and 6, provided with reflux condensers I5 and I6 respectively, the condenser I and the gas separator and receiver 3 are of conventional construction. The vapor separator 4 comprises atower having an open lower portion, an'interme'diate portion provided with open battles, and an upper portion provided with bubble trays, and is provided with a tar leg I8 and reflux condensers I9 and 20. Any appropriate cooling medium may be circulated through the heat exchange coilsin the reflux condensers 25, i5 and I6. The tar leg I8 makes possible the maintenance of a minimum liquid body within the lower portion of the vapor separator 4 without difliculties of regulation with respect to' tar discharge through connection 2i.

In operation, oil is supplied to the heating coils I and 2 through connections 3i and 32by means of either or both of pumps 22 and 23, and the hot oil products discharged from the heating coil 2 are introduced into the lower portion of the vapor separator 4 through connection 24 including a valve 25 for controlling the pressure maintained 'on the oil stream flowing'through the heating coils and for reducing the pressure on the hot oil products from the heating coil 2 as they are discharged into the vapor separator 4.- Either condensate or a condensate mixture from fractionating tower 5, a similar stock supplied through connection 26 by means ofpump 21, or'a mixture of the two'can be supplied-to connection 3| or 32 through valved connections 28 and 29 respectively. Similarly, either condensate or-a condensate mixture from fractionating tower 6, a similar stock supplied through connection 30 by means of pump 33, or a mixture of the two can be supplied to connection 3| or32 through valved connections 34 and 35 respectively. By regulation of the valves in connections 28, 29, 34 and 35 either or both of these stocks or stock mixtures can be supplied to either or both of, connections 3| and 32, to the exclusion of each other or'mixed in any desired proportions. The fractionating tower 5 is controlled by variation of the rate of cooling in the reflux condenser I5, or by introduction of an oil refluxing agent, a part of the condensate separated in fractionating tower '6 supplied through connection 36 or an extraneous stock supplied through connections 26 and 31 for example, or by both of these means conjointly. Similarly, the fractionating tower 6 is controlled by variation of the rate of cooling in the reflux condenser I6, or by introduction of an oil refluxing agent, a part of the condensate separated in the receiver 8 supplied through connections 38 and 39 or an extraneous stock supplied through connections 40 and 39 for example, or by both of these means conjointly. The frac- 7 tionating tower 6 may be by-passed by means of connection 4|. The condensate or condensate mixtures separated in either fractionating tower 5 or fractionating tower 6 may be discharged in whole or in part through connections 42 and 43 respectively. The vapor separator 4 is controlled 'either by regulated introduction of an oil cooling medium through either or both of connections 44 and 45, by regulated introduction of an oil refluxing agent through connection 46 or by variation of the rate of cooling in one or both 7 of the reflux condensers I9 and 2i], or by two or the hot oil products discharged from the second iii heating coil, are with advantage effected as described in United States Letters Patent Number 1,873,037, granted August 23, 1932 to Sinclair Refining Company on an application of Herman I. Ringgenberg. Condensate or condensate mixture separated in either or both of the fractionating towers 5 and 6 may be'supplied to the vapor separator 4 as an oil cooling medium through connection 41 and connections 48 and 49 respectively. The raw stock to be cracked is with advantage supplied, to connections 44 and or to both of these through connection 50 by means of pump 5|. It will be understood that the vapor mixture escaping from the upper part of the vapor separator 4 enters the lower part of the fractionating tower 5 through connection 52, that vapors escaping from the upper part of fractionating tower 5 enter either the lower part of fractionating tower 6 through connections 53 and 54 or the condenser 'I through connections 53, 4i and 55, and that vapors escaping from the upper part of fractionating tower 6 enter the condenser I through connections 56 and 55. Residual oil, or tar, is discharged from the tar leg I8 on the vapor separator 4 through connection 2|. The gasoline product is discharged from the gas separator and receiver 8 through connection 56 and uncondensed vapors and gases through connection 51.

Connection 58 is provided for the discharge of any water accumulating in the gas separator and receiver 8.

The following example of a typical operation embodying, the invention as practiced in apparatus such as that illustrated in the accompanying drawing will further illustrate the invention: 30 A. P.'I. Mid-Continent gas oil of which 18-29% boils off at 500 F. and 69-73% at 700 F. is supplied as cooling oil to the vapor separator 4 through connection 44 after passing through the reflux condenser I9 at a rate sufficient to maintain,-in conjunction with the reflux condenser 72!], temperatures at points F and G of about 765-'775 F. and 710-715 F. respectively, The gas oil so introduced into the vapor separator 4 is largely vaporized therein and condensed, together with the condensate separated in the fractionating towers 5 and 6.

The condensate separated in the fractionating connections, as cooling oil ture condensing in the condenser I to form a gasoline product having an end boiling point of about 400 F. and of which boils off at about 370 F. The condensate separated in the fractionating tower 5 is supplied to the heating coils I and 2, about four-fifths, by volume measured at 60 F., through connection 3! and about onefifth through connection 32. This condensate is supplied hot, at a temperature approximating that at which it leaves the fractionating tower 5, 600-650 F. for example, the temperature at points A and C corresponding to this temperature. In the heating coil l the oil stream is heated to a temperature, at point B, approximating 880-900 F. Because of the introduction of the secondary stream through connection 32 into the primary stream flowing from the heating coil 1 to the heating coil 2 through connection 59, the temperature of the combined stream, at point D, is reduced to a temperature approximating 835-855 F. The combined oil stream is heated in the heating coil 2 to a temperature, at point E, approximating 935-945 F. A pressure of 200-600 pounds per square inch is maintained on the oil stream as discharged from the heating coil 2, the pressure in connections 3| and 32 being higher than this by a margin sufficient to maintain fiow through the heating coils, and a pressure of about 60 pounds per square inch is maintained in the vapor separator 4. About 45-46% by volume on the raw stock of the gasoline product is recovered. The temperatures and pressures cited in the foregoing example represent a particularly advantageous embodiment of the process of the invention.

In carrying out the invention with the return of condensate or condensate mixtures or similar stocks from both of the fractionating towers 5 and 6 to the heating coils I and 2, the condensate from the fractionating tower 6 may be supplied alone to the heating coil l and the condensate from the fractionating tower 5 may be supplied to the heating coil 2, or a mixture of these condensates containing a higher proportion of the condensate from the fractionating tower 0 may be supplied to the heating coil 1! and such a mixture containing a lower proportion of the condensate from the fractionating tower 6 may be supplied to the heating coil 2.

I claim:

1. In the manufacture of gasoline, the improvement which comprises flowing a stream of oil through two heating zones directly connected in series without vapor separation in either zone into a vapor separator, maintaining a substantial superatmospheric pressure on the oil stream in both zones and maintaining a substantially lower pressure in the vapor separator, heating the oil stream to a high cracking temperature upwards of about 875 F. in the first zone, introducing a secondary stream of oil into the primary stream of oil flowing from the first to the second heating zone at a rate and temperature effective substantially to reduce the temperature of the primary stream, heating the-combined oil stream to a cracking temperature in the second zone substantially higher than the maximum temperature attained in said first zone, maintaining a temperature effective substantially to inhibit further cracking in the vapor separator, and separating in and taking off from the vapor separator a residual oil and a distillate fraction including the gasoline product.

2. In the manufacture of gasoline, the improvement which comprises flowing a stream of oil through two heating zones directly connected in series Without vapor separation in either zone into a vapor separator, maintaining a superatmospheric pressure upwards of about 200 pounds per square inch on the oil stream in both zones and maintaining a pressure not exceeding about pounds per square inch in the vapor separator, heating the oil stream to a cracking temperature approximating 880-900 F. in the first zone, introducing a secondary stream of oil into the primary stream of oil flowing from the first to the second heating zone at a rate and temperature effective to cool the primary stream to a temperature approximating 835-855 F., heating the combined oil stream to a cracking temperature approximating 935-945 F. in the second zone, maintaining a temperature approximating 700-775 F. in the vapor separator, and separating in and taking off from the vapor separator a residual oil and a distillate fraction including the gasoline product.

3. In the manufacture of gasoline, the improvement which comprises flowing a stream of oil through two heating zones directly connected in series without vapor separation in either zone into a vapor separator, maintaining a substantial superatmospheric pressure on the oil stream in both zones and maintaining a substantially lower pressure in the vapor separator, heating the oil stream to a cracking temperature upwards of about 875 F. in the first zone, introducing a secondary stream of oil into the primary stream of oil flowing from the first to the. second heating zone at a rate and temperature effective to reduce the temperature of the primary stream not less than about 40 F., heating the combined oil stream to a higher cracking temperature, not less than about 40 F. higher than that to which the oil stream is heated in the. first zone, in the second zone, maintaining a temperature not exceeding about 775 F. in the vapor separator, and separating in and taking off from the vapor separator a residual oil and a distillate fraction including the gasoline product.

4. In the manufacture of gasoline, the improvement which comprises flowing a stream of oil through two heating zones directly connected in series without vapor separation in either zone into a vapor separator, maintaining a substantial superatmospheric pressure on the oil stream in both zones and maintaining a substantially lower pressure in the vapor separator, heating the oil stream to a high cracking temperature upwards of about 875 F. in the first zone, introducing a secondary stream of oil not more refractory than that supplied to the first heating zone into the primary stream of oil flowing from the first to the second heating zone at a rateand temperature efiective substantially to reduce the temperature of the primary stream, heating the com- EDWARD W. ISOM. 

